In optical communications networks, a variety of different types of devices are used to couple light from the end of a fiber into the end of another fiber, to couple light from the end of a fiber onto an optical sensor (e.g., a photodiode) of a transceiver module, and to couple light from a light emitting device (e.g., a laser diode) of a transceiver module into an end of an optical fiber.
FIG. 1A illustrates a perspective view of a known multi-fiber connector module 31 manufacture by U.S. Conec Ltd. of Hickory, N.C. The connector module 31 has become known in the optical connector industry as the MTP® connector. The connector module 31 holds ends of receive fibers and has an optics system that couples light from a plurality of laser diodes of a transceiver module (not shown), or light from the ends of fibers held in an identical mated MTP connector module (not shown), into the ends of the receive fibers held in the connector module 31. Likewise, the connector module 31 holds the ends of transmit fibers and the optics system of the module 31 focuses light output from the ends of the transmit fibers onto a plurality of photodiodes of a transceiver module, or onto the ends of a plurality of fibers held in an identical mated MTP connector module.
The transmit and receive fibers held in the connector module 31 are part of a fiber ribbon 32 having a total of 4, 8, 12 or 24 optical fibers. A strain relief device 33 holds the fibers below the ends to prevent the fiber ends from moving in the event that mechanical loading on the cable occurs due to tugging or pulling on the cable. This prevents the integrity of the optical signals from being degraded due to a problem referred to in the optical communications industry as “wiggle” or “wiggle losses”.
The connector module 31 has an outer housing 34 and an inner housing 35. The inner housing has latching elements 36 thereon for securing the module 31 to a receptacle 61 of a transceiver module. A collar 32 surrounds the outer housing 34 of the connector module 31 and prevents the latching elements 36A and 36B from unlatching when the connector module 31 is connected to the transceiver module receptacle or to a receptacle that interconnects two MTP connector modules 31. The ends of the transmit and receive fibers are held within a multi-fiber ferrule 37 that extends slightly beyond the end 38 of the inner housing 35. The ends (not shown) of the fibers are polished and extend a very small distance beyond the end of the ferrule 37 such that the polished end of each fiber provides a flat optical element for coupling light between the polished end and an optical element (not shown) of the receptacle 61.
FIG. 1B illustrates a cutaway view of the MTP connector module 31 shown in FIG. 1A that reveals features inside of the connector module 31 and receptacle 61. Inside of the inner housing 35, the ferrule 37 is moveably secured and spring-loaded to allow it to move in the axial direction of the fibers. A spring (not shown) is located in the cylindrical groove 42 formed in the inner housing 35 of the connector module 31. When the connector module 31 is latched to the receptacle 61, the outer end 37A of the ferrule 37 is in abutment with the contact surface (not shown) of the receptacle 61. This contact surface of the receptacle 61 contains optical elements (not shown), which will be described below in more detail with reference to FIG. 1C. The abutment of the ferrule end 37A with this contact surface of the receptacle 61 exerts a force on the end 37A of the ferrule 37 in the axial direction of the fibers that causes the end 37B of the ferrule to press against and thereby compress the spring to allow the ferrule 37 to retract into the inner housing 35 of the connector module 31. The ferrule 37 retracts, floating against the surface of the receptacle 61 with zero clearance between them. This zero clearance between the ferrule end 37A and the surface of the receptacle 61 ensures that the flat optical elements comprising the polished ends of the fibers are in contact with the optics elements contained in the contact surface, which ensures efficient optical coupling.
FIG. 1C illustrates a cutaway view of the MTP connector module 31 shown in FIG. 1B with the connector module 31 connected to the receptacle 61. Only one side of the ferrule 37 is shown in FIG. 1C. The ferrule 37 has a cylindrical opening 37C formed in the left side thereof and a cylindrical opening (not shown) formed in the right side thereof for receiving cylindrical pins 62A and 62B that extend from the contact surface 63 of the receptacle 61 for guiding and alignment. The fibers (not shown) are positioned in respective grooves 41 formed in the ferrule 37 and secured thereto by an adhesive material. Latching elements 64A and 64B of the receptacle 61 engage latching elements 36A and 36B to lock the connector module 31 to the receptacle 61. The collar 32 is in sliding engagement with the outer housing of the connector module 31 and has an inner surface 39 that presses against the latching elements 64A and 64B to prevent them from disengaging from the latching elements 36A and 36B. This tight physical coupling and precision alignment of the connector module 31 and the receptacle 61 results in tight optical alignment, which, in turn, results in low optical losses and good signal integrity.
The MTP connector module 31 has been widely adopted due to its low wiggle loss, high optical coupling efficiency and high manufacturing yield. One of the disadvantages of the MTP connector module 31 is that it is relatively expensive due to the fact that the ends of the fibers must be polished and due to the fact that the parts must be manufactured with extremely high precision in order to achieve precise physical and optical alignment. Because of the precision with which physical alignment must be maintained in order to achieve the necessary optical coupling efficiency, any reduction in part precision will result in unacceptable optical losses. Attempts have been made to use cleaved fiber ends in the MTP connector module 31, but such attempts generally have been unsuccessful because they resulted in the connector modules having inconsistent optical coupling losses.
Another disadvantage of the MTP connector module 31 is that it is relatively inflexible with respect to accommodating changes in fiber density. In certain situations, there is a need to couple dense arrays of optical fibers to a large number of transceiver modules, such as in central offices where banks of transceiver modules used. In these types of environments, racks of transceiver modules are typically provided, with each rack having a front panel with receptacles configured to receive respective connector modules on the front and back sides of the panels. The receptacles align the respective connector modules on the front and back sides to enable light to be coupled between the ends of the fibers contained in the connector modules on the front side and the ends of the fibers contained in the connector modules on the back side. The fibers connected to the connector modules on the back side of the panel are then connected on opposite ends of the fibers to other respective connector modules, which are then connected to respective transceiver modules held in the racks.
If a need arises to increase the fiber density, this is typically accomplished by replacing the connector modules with connector modules that are designed to hold a larger number of fibers. For example, assuming the multi-fiber ferrule 37 of the MTP connector module 31 is a 2-by-12 configuration designed to hold a total of twenty-four fibers, if a need arises to increase the fiber density by, for example, 50%, the 2-by-12 MTP connector modules will typically be replaced with MTP connector modules having 4-by-12 configurations. This corresponds to a 100% increase in fiber density capability when only a 50% increase is needed. Thus, this solution is relatively inflexible with respect to accommodating changes in fiber density. Furthermore, MTP connector modules of this type are expensive, and therefore replacing them is costly. Also, having to replace connector modules increases yield losses.
In addition, this type of MTP connector module is also relatively inflexible with respect to its ability to accommodate different routing needs of different customers and with respect to its ability to accommodate re-routing needs. Because the ends of the fibers are permanently connected inside of the connector module, the fibers cannot be separated out based on routing or re-routing needs. Therefore, an entire 2-by-12 or an entire 4-by-12 connector module may need to be disconnected, removed and reconnected at another location. Consequently, routing and re-routing needs may not be able to be met, or may be able to be met only with considerable difficulty and cost.
Accordingly, a need exists for a multi-fiber connector module that enables changes in fiber density needs, routing needs and re-routing needs to be accommodated in a way that is relatively simple and inexpensive without having to replace connector modules. It would also be desirable to provide a multi-fiber connector module that can be made at relatively low cost by using cleaved fibers instead of polished fibers and that can be made with relatively inexpensive parts without sacrificing performance or manufacturing yield.